Connecting units of the above type are known, whose connectors comprise respective insulating casings defining respective numbers of cavities for housing mutually connectable male and female electric terminals respectively.
Connecting units of this type normally comprise a lever-and-slide coupling device, which, once the plug and socket connectors are brought together, is operated manually to couple the connectors with very little effort required.
The coupling device substantially comprises a slide fitted inside the plug connector casing to slide in a direction perpendicular to the coupling direction of the connectors; and an operating lever hinged to the same casing and fitted to the slide.
In one fairly commonly used embodiment, the slide is C-shaped and defined by an end wall perpendicular to the slide direction, and by two lateral walls extending perpendicularly from respective opposite end edges of the end wall, and which slide along relative lateral walls of the plug connector casing. Each lateral wall of the slide has a number of cam grooves engaged by respective outer pins on the plug connector to produce a relative engagement movement between the plug and socket connectors in the coupling direction when the slide moves in the slide direction.
The slide is normally retained by temporary locking means, e.g. releasable retaining members, in a preassembly position partly inserted inside the plug connector casing, and is moved into a full-insertion position inside the casing by rotating the operating lever from a raised to a lowered position about its hinge axis.
The lowered position of the lever, and consequently the full-insertion position of the slide, normally corresponds to complete coupling of the male and female terminals of the two connectors.
In the event one or more terminals are assembled wrongly inside the relative casings, however, the slide and lever may still be forced into the respective full-insertion and lowered positions, e.g. by breaking or deforming the contacting parts; in which case, the wrongly assembled terminals may escape detection during testing, e.g. because the position of the terminal is such as still to produce electrical contact, however precarious. In applications in which the connectors are subjected to vibration, as on vehicles, however, such contact is bound to be broken eventually, with all the obvious consequences this entails.